Generally, there are a number of types of apparatus which function to move an object in various directions. Among these apparatus are included power-operated shovels, cranes, personnel supporting booms, digger derricks and many others. These arrangements generally include a boom mounted at a first end to a platform, particularly a platform on a vehicle. The boom is attached to the platform such that it may be moved in a variety of directions. A second opposite end of the boom is typically adapted to mount one or more tools thereon. For instance, a shovel might be attached to the opposite end of the boom for digging. Alternatively, a bucket for carrying or supporting an individual might be attached to the end of the boom. Tools, such as tong-like pinchers or claws for grasping and steadying an article might be disposed at the end of the boom. Further, an auger or drill-like tool may be attached to the boom for drilling holes in the ground. The boom may be equipped with a winch and cable arrangement for lifting an article.
The boom is typically attached to the platform in such a way that the boom can move in several directions to position the tools as desired. For instance, the boom may be pivotally attached at its first end such that it can rotate in an arc or semicircle lying in a plane that is generally vertical, or in other words generally perpendicular to the surface on which the vehicle rests. Additionally, the boom may be pivotally attached at its first end to rotate about a generally vertical axis; that is, through an arc lying in a plane generally parallel to the surface on which the vehicle rests, typically horizontal.
It should be noted that throughout this application, the plane describing the surface on which the vehicle rests will be described as horizontal or generally horizontal for convenience reference to the drawings. Similarly, the plane perpendicular to the plane on which the vehicle rests will be described throughout as vertical. It is to be understood that the vehicle can be used on hills and the like and therefore the plane on which the vehicle rests will not necessarily be horizontal.
In addition to being movable in horizontal and vertical arcs, the boom may also be constructed and arranged to be extendable. That is, it may include telescopic portions which can be extended to increase the overall length of the boom.
By these and other movements, it will be possible to position the boom in such a manner that the tools (shovel, bucket, platform, claw, auger, winch line, etc.) will be at the desired position and can perform the desired tasks.
A digger derrick is such an apparatus. It is typically used to perform three primary functions: (1) to dig holes for poles for supporting power lines; (2) to provide tong-like grips and a winch arrangement for lifting and carrying a pole for supporting power lines, particularly to transport and position a pole into or out of one such hole; and (3) to support a worker or workers on a platform or in a bucket at the second end of the boom to lift the worker to perform necessary tasks on power lines.
Controls are required for causing the boom to perform the desired motions or functions. Typically, such apparatus can include a turret-like seat at the first end of the boom in which an operator is seated. A control panel is provided within reach of the operator. Typically, a control panel will be disposed in front of the operator, and a lever will be provided extending upward from the floor between the operator's legs. Alternatively, the operator's station and the controls may be remote from the rotational assembly of the boom, so that the operator does not move with the boom.
Typically, the controls are connected via a series of linkages to hydraulic valves which in turn are operationally connected to mechanisms for moving the boom in a particular fashion.
Safety is an important consideration in the design of such control arrangement. It is desirable that at least certain of the controls are operated in conjunction with a spring-loaded safety actuator or dead-man switch, that is, a switch which, unless activated, precludes the activation of the control. For instance, if the control for causing the boom to move in an up/down fashion (i.e. in a vertical arc) were connected to a control handle in conjunction with a dead-man switch, it would not be possible to activate the boom up/down control without simultaneously activating the dead-man switch.
Frequently, it is desired to move the boom through a rather complex motion or operation, requiring simultaneous activation of more than one of the movement controls. For instance, it may be desired to move the boom upward while at the same time moving it in an arc to the left of its original position. To do so would require activation of both the boom up/down movement control as well as the rotation control. Additionally, it may be desired to increase or decrease the length of the boom while traversing the desired path. Alternatively, it may be desired to move the boom through a series of motions in relatively rapid succession, rather than simultaneously. In short, it can be seen that it is desirable that the movement controls be arranged at the operator'disposal in a manner which conventionally allows the operator to activate more than one of the movement controls at the same time or sequentially. It is further desirable that the controls be operable in an intuitively sensible manner so that training time is reduced and safety of operation is enhanced.
For safety reasons, it can be seen that it is desirable that each of the movement controls be connected through a dead-man switch. Thus, it can be seen that what has been needed is a control operable with one hand which activates more than one, and preferably all, of the movement controls that govern movement of the boom. It would be desirable for that control to be operable with a single hand of the operator, so that the operator's other hand is free to activate controls to use particular tools on the boom (for instance, tong-like pinchers which need to be opened and closed to squeeze an object therebetween). It is further desirable that the control include a dead-man switch which would prevent activation of any and all of the movement controls when the dead-man switch is not activated.
It is further desirable that the control system be relatively maintenance free. It is desirable that the parts used in the system be resistant to wear, be relatively unaffected by severe temperature changes, and require little or infrequent lubrication.